A head support is commonly used on a seat such as a vehicle seat, to provide adequate support for the head of the person sitting in the seat, in particular to provide at least some safeguard for that person against the injury known as whiplash resulting for example from a rear-end impact against the vehicle. A typical form of head support comprises two head support carriers which are carried by the backrest portion of the seat. In another form of head support assembly, the head support member is arranged to be displaceable in a plane in parallel relationship with itself, generally along a centre line which is between the head support carriers and which extends normal to a notional line joining the head support carriers, transversely of the seat. Such an assembly is complicated in regard to handling however and the basic mechanism of the head support assembly is often not entirely satisfactory in terms of operation thereof.